4... h7h5 This is considered the best move by theory, stopping the dangerous advance of the kingside pawns. 5. f1d3 White reverts to a simpler strategy, exchanging bishops and trying to demonstrate that the inclusion of h4-h5 helps his position, since Black's king remains in danger with such a pawn formation. 5... f5d3  6. d1d3  6... d8a5 This check looks like a beginner's move, but it has the strategic idea of putting the queen on a6. White, naturally, doesn't want to exchange queens.